This invention relates to an image forming apparatus, and in particular, to a photoreceptor for use in an image forming apparatus and a manufacturing method thereof.
In a digital image forming apparatus, an image is formed through the processes of dot exposure by means of a laser, an array of light emitting diodes (LED""s), or the like, and development. On the other hand, a photoreceptor as an image carrying member is composed of a substrate made of metal such as aluminum and a photosensitive layer; however, there is a problem that, in exposure, it occurs an interference phenomenon between light reflected by the surface of the image carrying member and light reflected by the surface of the substrate, to influence image quality.
In an image forming apparatus capable of forming a multi-color image, generally speaking, by means of a cylindrical or belt-shaped image carrying member which is being rotated (moved), charging, exposure, and development are carried out for each of the colors, the component color toner images are successively superposed on the image carrying member, and the superposed color toner images are transferred onto a transfer paper sheet by one-time transfer operation, to form a multi-color image.
The exposure is carried out by the scanning of the surface of the image carrying member by a laser beam; in the case of a cylindrical image carrying member, it is formed of a cylindrical metallic substrate (mainly aluminum is used) coated with a photosensitive layer (an OPC, for example). However, the thickness of the photosensitive layer fluctuates with the surface state of the substrate fluctuating, and interference fringes (moire) caused by the laser beam reflected by the surface of the photosensitive layer and the laser beam reflected by the surface of the substrate are generated, to bring about defects in an image formed.
For a countermeasure of the above-mentioned problem, to roughen the surface of the substrate, to provide a subbing layer containing fine particles between the substrate and the photosensitive layer, etc. are considered.
It has been known as one of the above-mentioned countermeasures a method to apply cut working to the surface of the substrate with a cutting tool. By this method, caused by the feed pitch of the cutting tool, linear surface inequalities (linear projections and concavities) having a definite size are formed with a definite pitch in a definite direction on the surface of the substrate.
On the other hand, as regards the dot arrangement for image formation, a method of error diffusion is generally used; but in recent years, it has been put into practice to adopt an arrangement method in which dots are arranged with a definite pitch in one direction. By this dot arrangement, it is possible to make a dot image have a sufficient gradation.
However, in cases where linear surface inequalities having a definite size are formed with a definite pitch in a definite direction as described in the above, and an image is formed, using an arrangement method in which dots are arranged with a definite pitch in one direction, on an image carrying member having a substrate with its surface roughened to a definite roughness by cut working with a cutting tool, density unevenness caused by a moire is produced in some cases although it depends on the pitch of the linear surface inequalities on the substrate of the image carrying member and the pitch of the dots.
Further, the above-mentioned conventional technology has a limit in its application to an image formation process with improved gradation or the like, and it is difficult to prevent sufficiently the degradation of image quality. In particular, it has been proved that, in an image forming method in which the arrangement of dots making up an image was made denser in one direction for the purpose of improving the gradation representation performance, a moire caused by the interference between the arrangement of dots and the linear surface inequalities on the substrate was produced to lower the image quality.
It is an object of this invention to solve such a problem and provide an image forming apparatus capable of forming a high-quality image having no density unevenness.
It is another object of this invention to provide an image forming apparatus having the generation of density unevenness suppressed by the practice of image formation with the pitch of the linear surface inequalities of the substrate of an image carrying member and the arrangement of dots taken into consideration.
The above-mentioned object can be accomplished by any one of the structures of the invention described below.
(1) An image forming apparatus which is equipped with a photoreceptor having a substrate with its surface subjected to surface processing with a cutting tool and a photosensitive layer formed on said substrate and an exposure means having a light source for emitting a light beam, and carries out exposure in a manner of an arrangement of dots through main scanning by the deflection of said light beam and the sub-scanning by the movement of said photoreceptor, characterized by said exposure means carrying out scanning exposure with a spatial frequency of the arrangement pitch of dots of 4 dots/mm in said main scanning direction, and the surface roughness Rz of said substrate in said main scanning direction being not greater than 1.5 xcexcm.
(2) An image forming apparatus which is equipped with a photoreceptor having a substrate with its surface subjected to surface processing with a cutting tool and a photosensitive layer formed on said substrate and an exposure means having a light source for emitting a light beam, and carries out exposure in a manner of an arrangement of dots through main scanning by the deflection of said light beam and the sub-scanning by the movement of said photoreceptor, characterized by said exposure means carrying out scanning exposure with a spatial frequency of the arrangement pitch of dots of 4 dots/mm in said main scanning direction, and said substrate, as regards its cross-sectional surface shape in said main scanning direction, having substantially no projections and concavities of a period corresponding to the feed pitch of the cutting tool in said surface processing with a cutting tool.
(3) An image forming apparatus which is equipped with a photoreceptor having a substrate with its surface subjected to surface processing with a cutting tool and a photosensitive layer formed on said substrate and an exposure means having a light source for emitting a light beam, and carries out exposure in a manner of an arrangement of dots through main scanning by the deflection of said light beam and the sub-scanning by the movement of said photoreceptor, characterized by said exposure means carrying out scanning exposure with a spatial frequency of the arrangement pitch of dots of 4 dots/mm in said main scanning direction, and said substrate having a surface subjected to a surface processing satisfying the following condition:
Rxe2x88x92R cos [{(X/2)/2xcfx80R}xc3x97360] less than 0.001, 
where R denotes the radius of curvature (mm) of the edge corner of a cutting tool used in said surface processing, and X denotes the feed pitch of the cutting tool (mm) in said surface processing.
(4) An image forming apparatus as set forth in any one of the above-mentioned structures (1) to (3), characterized by the aforesaid exposure means carrying out exposure with a dot arrangement such that the dot density in the sub-scanning direction is made larger than the dot density in the main scanning direction.
(5) An image forming apparatus as set forth in any one of the above-mentioned structures (1) to (4), characterized by comprising a developing means for developing a latent image using a toner composed of toner particles having a number-average particle diameter of 2 xcexcm to 7 xcexcm.
(6) An image forming apparatus as set forth in any one of the above-mentioned structures (1) to (5), characterized by the aforesaid substrate being made of a metallic cylinder.
(7) A method of manufacturing a substrate for a photoreceptor made of a metallic cylinder characterized by comprising the step of carrying out a surface processing to be applied to its surface satisfying the following condition:
Rxe2x88x92R cos [{(X/2)/2xcfx80R}xc3x97360] less than 0.001, 
where R denotes the radius of curvature (mm) of the edge corner of a cutting tool used in said surface processing, and X denotes the feed pitch of the cutting tool (mm) in said surface processing.
(8) A substrate for a photoreceptor characterized by being manufactured by a manufacturing method of a substrate for a photoreceptor wherein a surface processing to be applied to its surface satisfying the following condition is carried out:
Rxe2x88x92R cos [{(X/2)/2xcfx80R}xc3x97360] less than 0.001, 
where R denotes the radius of curvature (mm) of the edge corner of a cutting tool used in said surface processing, and X denotes the feed pitch of the cutting tool (mm) in said surface processing.
(9) A substrate for a photoreceptor characterized by being manufactured by a manufacturing method of a substrate for a photoreceptor wherein a surface processing to be applied to its surface satisfying the following condition is carried out:
Rxe2x88x92R cos [{(X/2)/2xcfx80R}xc3x97360] less than 0.001, 
where R denotes the radius of curvature (mm) of the edge corner of a cutting tool used in said surface processing, and X denotes the feed pitch of the cutting tool (mm) in said surface processing; and a photoreceptor characterized by comprising a photosensitive layer formed on said substrate.
(10) A photoreceptor as set forth in the above-mentioned structure (9), characterized by the aforesaid photoreceptor having a thickness of 10 xcexcm to 30 xcexcm.
(11) An image forming apparatus which forms a latent image composed of a plurality of dots through the scanning of a cylindrical image carrying member in the lengthwise direction by a light beam emitted from a light source to make a latent image component in the main scanning direction, and forms a plurality of said latent image components in the rotating direction of the cylindrical image carrying member, that is, in the sub-scanning direction to form a latent image, characterized by the surface of the substrate of said image carrying member having linear surface inequalities (projections and concavities) caused by the feed pitch of the cutting tool formed in cut working, said latent image consisting of a plurality of dot lines formed in the sub-scanning direction arrayed at equal intervals, that is, with a pitch in the main scanning direction, and each of said plurality of dot lines being formed at an angle not smaller than a specified angle with the direction of the linear surface inequalities formed on the surface of said substrate of said image carrying member.
(12) An image forming apparatus as set forth in the structure (11), characterized by the aforesaid specified angle being not smaller than 30xc2x0.
(13) An image forming apparatus which forms a latent image composed of a plurality of dots through the scanning of a cylindrical image carrying member in the lengthwise direction by a light beam emitted from a light source to make a latent image component in the main scanning direction, and forms a plurality of said latent image components in the rotating direction of the cylindrical image carrying member, that is, in the sub-scanning direction to form a latent image, wherein the surface of the substrate of said image carrying member has linear surface inequalities caused by the feed pitch of the cutting tool formed in cut working, said latent image consists of a plurality of dot lines formed in the sub-scanning direction arrayed at equal intervals in the main scanning direction, and each of said plurality of dot lines is formed at an angle not smaller than a specified angle with the direction of the linear surface inequalities formed on the surface of said substrate of said image carrying member, characterized by one or both of said feed pitch of the cutting tool and said pitch of the array of said dot lines in the main scanning direction being determined so as to make the difference between the number of said surface inequalities per unit length and the number of said dot lines per unit length not smaller than a specified number.
(14) An image forming apparatus as set forth in the structure (13), characterized by the aforesaid specified number being not less than 1 line per 1 mm.
(15) An image forming apparatus as set forth in the structure (13), characterized by the aforesaid specified angle being not larger than 30xc2x0.
(16) An image forming apparatus as set forth in any one of the structures (11) to (15), characterized by the surface of the substrate of the aforesaid image carrying member having finer surface inequalities between the projections formed by the feed pitch of the cutting tool in cut working.